What is the first sign of hypothermia as core body temperature decreases?

Shivering is recognized as the first sign of hypothermia as core body temperature begins to decrease. This physiological response occurs when the body's temperature drops significantly below normal levels, prompting the body to engage in involuntary muscle contractions to generate heat and maintain its core temperature. Shivering can begin at a body temperature around 98.6°F (37°C) and becomes more pronounced as the temperature falls further.

This adaptive mechanism is vital in helping to warm the body during exposure to cold environments. As hypothermia progresses, other symptoms may develop, but shivering serves as an early warning sign that immediate action is needed to prevent further heat loss and potential serious health issues related to hypothermia.